Exhaust system of multi-cylinder internal combustion engine

ABSTRACT

A plurality of upstream main exhaust passages extend from cylinders of an engine. A downstream main exhaust passage is connected to the upstream main exhaust passages. A main catalytic converter is mounted in the downstream main exhaust passage. A plurality of upstream bypass exhaust passages extend from the upstream main exhaust passages. Each upstream bypass exhaust passage has a sectional area smaller than that of the corresponding upstream main exhaust passage. A downstream bypass exhaust passage is connected to the upstream bypass exhaust passages and has a downstream end connected to the downstream main exhaust passage at a position upstream of the main catalytic converter. An auxiliary catalytic converter is mounted in the downstream bypass exhaust passage. A gas flow switching device is provided which is capable of forcing the exhaust gas from the cylinders of the engine to flow toward the upstream bypass exhaust passages when assuming a given operation position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to exhaust systems of amulti-cylinder internal combustion engine, that have a catalyticconverter for purifying the exhaust gas from the engine, and moreparticularly to the exhaust systems of a type that has main andauxiliary catalytic converters wherein when, like in a condition justafter cold starting of the engine, the main catalytic converter is notsufficiently activated, the exhaust gas is led to the auxiliarycatalytic converter that is easily activated.

2. Description of the Related Art

Usually, in motor vehicles powered by an internal combustion engine, theexhaust system of the engine is arranged beneath a floor of the vehicleand has a catalytic converter installed therein. If the catalyticconverter is arranged in a relatively downstream position of the system,the converter takes a long time to be heated to a sufficient level forthe gas purifying operation thereof particularly in a condition justafter cold starting of the engine. That is, for such long time, thecatalytic converter fails to exhibit its normal gas purifying work.However, if, for solving the above-mentioned drawback, the catalyticconverter is arranged in a relatively upstream position of the system,that is, a position near the engine, another drawback tends to arisewherein due to attack of heat of the engine and the highly heatedexhaust gas from the engine, the durability of the catalytic converteris lowered.

In order to solve the above-mentioned drawbacks, various measures havebeen proposed, one of which is disclosed in Japanese Laid-open PatentApplication (Tokkaihei) 5-321644. In this measure, a main passageextends from an exhaust manifold of the engine to a main catalyticconverter. A bypass passage having an auxiliary catalytic converterinstalled therein extends from an upstream part of the main passage to adownstream part of the same. A switch valve is arranged at the upstreampart of the main passage to open and close the main and bypass passagesselectively, and a controller is connected to the switch valve. Inoperation, just after cold starting of the engine, the controllercontrols the switch valve to introduce the exhaust gas from the engineinto the bypass passage.

Since, in this measure, the auxiliary catalytic converter is positionedat a relatively upstream portion of the exhaust system, earlieractivation of the auxiliary catalytic converter is expected, whichinduces earlier exhaust gas purifying work by the exhaust system.

SUMMARY OF THE INVENTION

In the measure of the above-mentioned patent application publication,the gas inlet port of the bypass passage is positioned downstream of abranch junction portion of the exhaust manifold. That is, from a portionthat is downstream of the junction portion where exhaust gas paths ofall cylinders of the engine are joined, there extend the main and bypasspassages in parallel. Thus, even though the auxiliary catalyticconverter can take a more upstream position than the main catalyticconverter, the distance from the exhaust port of each cylinder to theauxiliary catalytic converter can not be so short, and thus actually,the earlier exhaust gas purifying work in the cold starting of theengine is not effectively carried out.

Because of branching of the bypass passage from the downstream positionof the exhaust manifold, the exhaust manifold that has a marked thermalcapacity causes the temperature of the exhaust gas led into the bypasspassage to be lowered, which obstructs the earlier exhaust gas purifyingwork of the auxiliary catalytic converter.

Furthermore, since the modernized exhaust manifolds are designed andconstructed to avoid or at least minimize an exhaust interference, it isdifficult to shorten the distance to the auxiliary catalytic converterfrom the inlet of the bypass passage. That is, in case of an exhaustmanifold for in-line four cylinder engines, a so-called “4-2-1”connection type is currently employed wherein branches for #1 and #4cylinders form one unit and branches for #2 and #3 cylinders form theother unit, and these two units are united at an outlet portion of themanifold. As is easily known, in this type exhaust manifold, it isdifficult to reduce the overall length. The above-mentioned “4-2-1”connection type tends to have a complicated construction of themanifold, which increases the thermal capacity of the same.

It is therefore an object of the present invention to provide an exhaustsystem of a multi-cylinder internal combustion engine, which is free ofthe above-mentioned drawbacks.

In accordance with a first aspect of the present invention, there isprovided an exhaust system of a multi-cylinder type internal combustionengine, which comprises a plurality of upstream main exhaust passagesconnected to cylinders of the engine respectively; a downstream mainexhaust passage that is connected to the upstream main exhaust passages;a main catalytic converter mounted in the downstream main exhaustpassage; a plurality of upstream bypass exhaust passages that extendfrom the upstream main exhaust passages respectively, each upstreambypass exhaust passage having a sectional area smaller than that of thecorresponding upstream main exhaust passage; a downstream bypass exhaustpassage that is connected to the upstream bypass exhaust passages; thedownstream bypass exhaust passage having a downstream end connected tothe downstream main exhaust passage at a position upstream of the maincatalytic converter; an auxiliary catalytic converter mounted in thedownstream bypass exhaust passage; and a gas flow switching device thatis capable of forcing the exhaust gas from the cylinders of the engineto flow toward the upstream bypass exhaust passages when assuming agiven operation position.

In accordance with a second aspect of the present invention, there isprovided an exhaust system of an in-line four cylinder internalcombustion engine, which comprises first, second, third and fourthupstream main exhaust passages extending from first, second, third andfourth cylinders of the engine, the first and fourth cylinders beingthose whose firing order is not successive and the second and thirdcylinders being those whose firing order is not successive; a firstintermediate main exhaust passage that is provided by joining downstreamends of the first and fourth upstream main exhaust passages; a secondintermediate main exhaust passage that is provided by joining downstreamends of the second and third upstream main exhaust passages; adownstream main exhaust passage that is provided by joining downstreamends of the first and second intermediate main exhaust passages; a maincatalytic converter mounted in the downstream main exhaust passage;first and second upstream bypass exhaust passages respectively extendingfrom upstream portions of the first and second upstream main exhaustpassages; third and fourth upstream bypass exhaust passages respectivelyextending from upstream portions of the third and fourth upstream mainexhaust passages; a first intermediate bypass exhaust passage that isprovided by jointing downstream ends of the first and second upstreambypass exhaust passages; a second intermediate bypass exhaust passagethat is provided by joining downstream ends of the third and fourthupstream bypass exhaust passages; a downstream bypass exhaust passagethat is provided by joining downstream ends of the first and secondintermediate bypass exhaust passages, the downstream bypass exhaustpassage having a downstream end connected to the downstream main exhaustpassage at a position upstream of the main catalytic converter; and anauxiliary catalytic converter mounted in the downstream bypass exhaustpassage.

In accordance with a third aspect of the present invention, there isprovided an exhaust system of an in-line four cylinder internalcombustion engine, which comprises first, second, third and fourthupstream main exhaust passages extending from first, second, third andfourth cylinders of the engine, the first and fourth cylinders beingthose whose firing order is not successive and the second and thirdcylinders being those whose firing order is not successive; a firstintermediate main exhaust passage that is provided by joining downstreamends of the first and fourth upstream main exhaust passages; a secondintermediate main exhaust passage that is provided by joining downstreamends of the second and third upstream main exhaust passages; adownstream main exhaust passage that is provided by joining downstreamends of the first and second intermediate main exhaust passages; a maincatalytic converter mounted in the downstream main exhaust passage;first and second upstream bypass exhaust passages respectively extendingfrom upstream portions of the first and second upstream main exhaustpassages; third and fourth upstream bypass exhaust passages respectivelyextending from upstream portions of the third and fourth upstream mainexhaust passages; a first intermediate bypass exhaust passage that isprovided by jointing downstream ends of the first and second upstreambypass exhaust passages; a second intermediate bypass exhaust passagethat is provided by joining downstream ends of the third and fourthupstream bypass exhaust passages; a downstream bypass exhaust passagethat is provided by joining downstream ends of the first and secondintermediate bypass exhaust passages, the downstream bypass exhaustpassage having a downstream end connected to the downstream main exhaustpassage at a position upstream of the main catalytic converter; anauxiliary catalytic converter mounted in the downstream bypass exhaustpassage; and switch valves respectively mounted in the first, second,third and fourth upstream main exhaust passages.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will becomeapparent from the following description when taken in conjunction withthe accompanying drawings, in which:

FIG. 1 is a conceptual drawing showing an exhaust system of a firstembodiment of the present invention;

FIG. 2 is a side view of the exhaust system of the first embodiment;

FIG. 3 is a bottom view of an exhaust manifold employed in the firstembodiment;

FIG. 4 is a top view of the exhaust manifold employed in the firstembodiment;

FIG. 5 is an enlarged sectional view of a valve unit and its nearbyportion;

FIG. 6 is a front view of the valve unit;

FIG. 7 is a view of a link mechanism for synchronously actuating twoswitch valves that constitute the valve unit;

FIG. 8 is a sectional view of a valve unit employed in an exhaust systemof a second embodiment of the present invention;

FIG. 9 is a sectional view of a valve unit employed in an exhaust systemof a third embodiment of the present invention;

FIG. 10 is a sectional view of a valve unit employed in an exhaustsystem of a fourth embodiment of the present invention;

FIG. 11 is a sectional view of a valve unit employed in an exhaustsystem of a first embodiment of the present invention;

FIG. 12 is a view similar to FIG. 1, but showing an exhaust system of asixth embodiment of the present invention;

FIG. 13 is a sectional view of an essential portion of an exhaust systemof a seventh embodiment of the present invention, in which an auxiliarycatalytic converter is directly connected to a cylinder head of anengine; and

FIG. 14 is a conceptional drawing showing an exhaust system of a seventhembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following, various embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

For ease of understanding, various directional terms, such as, right,left, upper, lower, rightward and the like are used in the followingdescription. However, these terms are to be understood with respect toonly a drawing or drawings on which the corresponding part or portion isshown.

Referring to FIG. 1, there is shown a conceptual drawing of an exhaustsystem 100 of a first embodiment of the present invention. In thisembodiment, an in-line four-cylinder internal combustion engine isemployed for embodying the invention.

Four cylinders 1, viz., #1, #2, #3 and #4 are aligned in a cylinderblock of the engine. From each cylinder 1, there extends an upstreammain exhaust passage 2.

It is to be noted that upstream main exhaust passage 2 is a passage thatextends from an exhaust valve (not shown) of the engine to a downstreampart where an after-mentioned junction portion with the other upstreammain exhaust passage 2 is provided.

As shown, upstream main exhaust passages 2 from cylinders #1 and #4whose firing order is not successive are joined by a first intermediatemain exhaust passage 3A, and upstream main exhaust passages 2 fromcylinders #2 and #3 whose firing order is not successive are joined by asecond intermediate main exhaust passage 3B.

In each of the joined portions, there is installed a switch valve 4A or4B. As will be described in detail hereinafter, switch valves 4A and 4Bare controlled by a single actuator.

That is, when the engine is in a condition just after cold staring,switch valves 4A and 4B are controlled by the actuator to take theirclose position blocking a fluid communication between each main exhaustpassage 2 and corresponding intermediate main exhaust passage 3A or 3B,and at the same time, blocking a fluid communication between the twoupstream main exhaust passages 2 which are joined.

As will be described in detail hereinafter, the two switch valves 4A and4B constitute a valve unit 5A (see FIGS. 2 and 5).

As is seen from FIG. 1, first and second intermediate main exhaustpassages 3A and 3B extending from valve unit 5 are joined at a junctionportion 6 and a downstream main exhaust passage 7 extends downstreamfrom the junction portion 6.

In downstream main exhaust passage 7, there is installed a maincatalytic converter 8 that includes a three-way catalyst and a HC(hydrocarbon) trapping catalyst. This main catalytic converter 8 isarranged beneath a vehicle floor and has a sufficient capacity.

Thus, the four upstream main exhaust passages 2, the two intermediatemain exhaust passages 3A and 3B, the downstream main exhaust passage 7and the main catalytic converter 8 constitute a main exhaust passagestructure through which the exhaust gas from the engine is permitted toflow in a normal operation condition of the engine. That is, in suchnormal operation condition, the “4-2-1” connection type passagearrangement of the exhaust system is defined, and thus, the chargingefficiency of the cylinders is increased with the aid of the exhaustdynamic effect.

As is seen from FIG. 1, from a branched portion 12 of each upstream mainexhaust passage 2, there extends an upstream bypass exhaust passage 11.

It is to be noted that the branched portion 12 is provided in thepassage 2 as upstream as possible. More specifically, the branchedportion 12 should be provided at least in a range that is upstream to a½ point of the entire length of upstream main exhaust passage 2.

Each upstream bypass exhaust passage 11 has a sectional area that issufficiently smaller than that of the corresponding upstream mainexhaust passage 2.

As shown, upstream bypass exhaust passages 11 from the main exhaustpassages 2 from cylinders #1 and #2 are united at a junction portion 13,and a first intermediate bypass exhaust passage 14A extends downstreamfrom the junction portion 13. Similarly, upstream bypass exhaustpassages 11 from the main exhaust passages 2 from cylinders #3 and #4are joined at a junction portion 13, and a second intermediate bypassexhaust passage 14B extends downstream from the junction portion 13.Each bypass exhaust passage 11 is made as short as possible.

As shown, the two intermediate bypass exhaust passages 14A and 14B areunited at a junction portion 15, and a downstream bypass exhaust passage16 extends downstream from junction portion 15. The downstream bypassexhaust passage 16 is led to a junction portion 17 provided on thedownstream main exhaust passage 7 at a position upstream of maincatalytic converter 8, as shown.

In downstream bypass exhaust passage 16, there is installed an auxiliarycatalytic converter 18 that includes a three-way catalyst. Thisauxiliary catalytic converter 18 is arranged in the bypass exhaustpassage as upstream as possible. In other words, the length of eachbypass exhaust passage between branched portion 12 and junction portion15 should be made as short as possible.

If desired, the four upstream bypass exhaust passages 11 may be joinedat a position just upstream of auxiliary catalytic converter 18 withoutthe aid of the above-mentioned two intermediate bypass exhaust passages14A and 14B. However, when considering a fixed positioning between eachbranched portion 12 and auxiliary catalytic converter 18, theabove-mentioned “4-2-1” united type passage arrangement is preferable inthe present invention. That is, in this type, the entire length of thepassages practically used can be reduced, and thus, the piping used canhave a reduced thermal capacity and a reduced heat radiation area to theatmosphere.

As shown in FIG. 1, auxiliary catalytic converter 18 comprises a firstcatalyst part 18 a and a second catalyst part 18 b which are arranged intandem. Between these two parts 18 a and 18 b, there is defined acertain clearance 19 to which an inlet part of EGR (viz., exhaust gasrecirculation) passage 20 is exposed. Although not shown in the drawing,an outlet part of this EGR passage 20 is exposed to a part of an airintake system of the engine through an EGR control valve. That is,during operation of the engine, part of the exhaust gas is picked upfrom the clearance 19 and led to the air intake system.

It is to be noted that auxiliary catalytic converter 18 has a smallcapacity as compared with main catalytic converter 8, and is of a typethat can exhibits a sufficient activation even in a relatively coldcondition.

When, in operation, the engine is in a condition just after a coldstaring, that is, when the temperature of the exhaust gas from theengine is not sufficiently high, the actuator (not shown) causes the twoswitch valves 4A and 4B to take a close position, thereby blocking themain exhaust passage. Under this condition, the exhaust gas from theengine is entirely led to the four upstream bypass exhaust passages 11from the branched portions 12 and then led to auxiliary catalyticconverter 18 through the two intermediate bypass exhaust passages 14Aand 14B.

Since auxiliary catalytic converter 18 is positioned at the upstreamside of the exhaust system, that is, near the cylinders #1, #2, #3 and#4, and a smaller capacity, the converter 18 is heated quickly and thusactivated quickly, and thus a sufficient exhaust purifying operation ofthe auxiliary catalytic converter 18 can start early.

Because, under this condition, each switch valve 4A or 4B isolates thepaired upstream main exhaust passages 2, undesired exhaust gastemperature reduction, that would be caused by a reciprocating movementof the exhaust gas between the paired upstream main exhaust passages 2through the switch valve 4A or 4B, is suppressed or at least minimized.This promotes the quick activation of the auxiliary catalytic converter18.

Furthermore, since, under this condition, the exhaust gas led into EGRpassage 20 is the gas that has been purified or cleaned by firstcatalyst part 18 a of the auxiliary converter 18, the EGR system,particularly, the EGR gas control valve of the same can be protectedfrom solid deposit and contamination.

While, when, due to continuous operation of the engine, the exhaust gasfrom the engine shows a sufficiently high temperature, the actuatorcauses the two switch valves 4A and 4B to take an open position, therebyestablishing an open condition of the main exhaust passage.

With this, the exhaust gas from the engine is mainly led into the fourupstream main exhaust passages 2 and into the main catalytic converter 8through the paired intermediate main exhaust passages 3A and 3B. Becauseeach upstream bypass exhaust passage 11 has a cross sectional area thatis smaller than that of the corresponding upstream main exhaust passage2, and because of presence of the auxiliary catalytic converter 18 inthe bypass exhaust system, almost all of the exhaust gas from the engineis forced to flow in the main exhaust system. Thus, in this case, theauxiliary catalytic converter 18 is free of a thermal degradation.Furthermore, since the bypass exhaust passage is opened but in a smalldegree, a part of the exhaust gas is permitted to enter the bypassexhaust passage when, under a high speed and high load operationcondition, a larger amount of exhaust gas is produced by the engine.This prevents lowering of charging efficiency of the cylinders caused bya back pressure.

As is described hereinabove, the main exhaust passage system is in theform of “4-2-1” united type arrangement, and thus, increase in thecharging efficiency of the cylinders is achieved with the aid of theexhaust dynamic effect.

While, the bypass exhaust passage system is arranged in theabove-mentioned manner without taking the exhaust interference avoidanceinto a consideration. However, since each upstream bypass exhaustpassage 11 used has a sufficiently smaller sectional area, the exhaustinterference inevitably induced by a communication with thecorresponding cylinder can be reduced to a very small degree. If thesectional area of upstream bypass exhaust passage 11 is made larger thana predetermined high degree, a marked lowering of the chartingefficiency would take place due to the exhaust interference. While, ifthe sectional area is made smaller than a predetermined low degree, theamount of exhaust gas during the time when switch valves 4A and 4B arekept in their close position is excessively reduced, and thus, theoperation range in which the bypass exhaust system can be practicallyoperated is excessively reduced.

Thus, actually, the sectional area of upstream bypass exhaust passage 11should have a range that varies in accordance with an enginedisplacement. Examination has revealed that when the engine has adisplacement of 2000 cc, a sufficient performance is obtained from thebypass exhaust system with an inner diameter of upstream bypass exhaustpassage 11 that ranges from 5 mm to 15 mm.

If operation of the EGR system is carried out under the open position ofswitch valves 4A and 4B, the exhaust gas for the recirculation is pickedup from auxiliary catalytic converter 18. If, under this EGR operation,a part of the exhaust gas flowing in downstream main exhaust passage 7flows backward in downstream bypass exhaust passage 16, the exhaust gasin the passage 16 is forced to pass through second catalyst part 18 b ofthe converter 18, and thus, the exhaust gas used for the EGR system isnot contaminated and thus, the EGR system, particularly, the EGR gascontrol valve is protected from solid deposit and contamination. Theexhaust gas flowing backward in downward bypass exhaust passage 16 isrelatively slow in flow speed, and thus, the exhaust gas can stay insecond catalyst part 18 b for a sufficient time. Thus, second catalystpart 18 b may have a size or length smaller or shorter than firstcatalyst part 18 a, as shown.

In the following, detailed explanation on the exhaust system 100 of thefirst embodiment will be made with reference to FIG. 2.

In the drawing, denoted by numeral 31 is an internal combustion engine,which comprises a cylinder block 32 and a cylinder head 33 mounted oncylinder block 32. The engine 31 is transversely mounted in an engineroom of a motor vehicle. In the drawing, a right side of engine 31 facesrearward of the vehicle, and thus, the right side will be referred to aback side in the following description.

An exhaust manifold 34 is mounted to the back side of cylinder head 33,that defines therein the above-mentioned four upstream main exhaustpassages 2. To a rear end of exhaust manifold 34, there is mounted thevalve unit 5A that is equipped with the two switch valves 4A and 4B.Extending downstream from valve unit 5A is a front exhaust tube 35 thatconstitutes the above-mentioned downstream main exhaust passage 7. Anupstream portion of front exhaust tube 35 has therein two parallelpassages that constitute the above-mentioned intermediate main exhaustpassages 3A and 3B. Main catalytic converter 8 is mounted on the frontexhaust tube 35 at a position downstream of the parallel passages 3A and3B.

As shown in FIG. 2, auxiliary catalytic converter 18 and its associatedparts 11, 14A, 14B, 16 and 20 are arranged below the main exhaust systemthat extends rearward from cylinder head 33 of the engine 31. Auxiliarycatalytic converter 18 is placed in the engine room in front of frontexhaust tube 35. Thus, under running of the associated motor vehicle,auxiliary catalytic converter 18 is effectively cooled by air flow thatis produced when the vehicle runs, and thus, overheating of thisconverter 18 is suppressed.

As shown, each upstream bypass exhaust passage 11 is branched at thebranched portion 12 from the corresponding upstream main exhaust passage2 in such a manner as to define an acute angle therebetween, whichsmoothes the gas flow from the main passage 2 to the bypass passage 11at the time when switch valves 4A and 4B take their close position. Itis to be noted that downstream portions of the two bypass exhaustpassages 11 are united to constitute the first intermediate bypassexhaust passage 14A, and downstream portions of the other two bypassexhaust passages 11 are united to constitute the second intermediatebypass exhaust passage 14B.

The arrangement of the exhaust system 100 of the first embodiment willbe much clearly understood from FIGS. 3 and 4 of the accompanyingdrawings.

FIG. 3 shows a bottom view of exhaust manifold 34, and FIG. 4 shows atop view of the same.

As is seen from these drawings, exhaust manifold 34 comprises fourbranches 41, 42, 43 and 44 that constitute upstream main exhaustpassages 2 respectively, two mounting flanges 45 and 46 that are to befixed to the cylinder head of the engine and have openings (no numerals)to which upstream ends of branches 41, 42, 43 and 44 are exposedrespectively, and four bypass tubes 11 that extend from the upstreamportions (12) of corresponding branches 41, 42, 43 and 44 to constitutethe upstream bypass exhaust passages 11 respectively.

As shown, the two bypass tubes 11 extending from branches 41 and 42 fromcylinders #1 and #2 are united at their downstream portions toconstitute a united passage portion that corresponds to the firstintermediate bypass passage 14A, and the other two bypass tubes 11extending from branches 43 and 43 from cylinders #3 and #4 are united attheir downstream portions to constitute another united passage portionthat corresponds to the second intermediate bypass passage 14B.

These two united passage portions 14A and 14B have a mounting flange 47that has an opening (no numeral) to which downstream ends of the passageportions 14A and 14B are exposed. Although not shown in these drawings,an inlet portion of the above-mentioned auxiliary catalytic converter 18is secured to mounting flange 47.

As will be understood from FIGS. 3 and 4, at a downstream portion offour branches 41, 42, 43 and 44 of exhaust manifold 34, there areprovided two mounting flanges 48A and 48B which are united.

As is seen from FIG. 3, mounting flange 48A has two openings to whichbranches 41 and 44 are connected respectively, and the other mountingflange 48B has two openings to which the other branches 42 and 43 areconnected respectively. If desired, in place of using the two mountingflanges 48A and 48B, a single mounting flange may be used. In this case,the mounting flange has four isolated openings to which the fourbranches 41, 44, 42 and 43 are connected respectively in theabove-mentioned manner.

Referring to FIGS. 5 and 6, there is shown the detail of valve unit 5Athat is operatively connected to the two mounting flanges 48A and 48B.

As is well seen from FIG. 5, valve unit 5A comprises a casing 51 thathas four openings, which are a first pair of openings 52 and 55 and asecond pair of openings 53 and 54. Upon connection of the casing 51 withthe two mounting flanges 48A and 48B, the two openings of mountingflange 48A are connected to the paired openings 52 and 55, and the twoopenings of the other mounting flange 48B are connected to the otherpaired openings 53 and 54.

As is seen from FIG. 5 and as has been mentioned hereinabove, from valveunit 5A, there extends the front exhaust tube 35 that has at itsupstream portion two parallel passages 3A and 3B (which are theabove-mentioned first and second intermediate main exhaust passages 3Aand 3B) partitioned by an axially extending partition wall 59. One ofthe two parallel passages 3A and 3B is communicated with the pairedopenings 52 and 55, and the other one of the parallel passages 3A and 3Bis communicated with the other paired openings 53 and 54.

Behind the paired openings 52 and 55, there is pivotally arranged afirst switch valve 4A that comprises a pivot shaft 56 actuated by anafter-mentioned actuator, a body holder 57 integral with pivot shaft 56and a flat rectangular valve body 58 fitted to body holder 57.Similarly, behind the other paired openings 53 and 55, there ispivotally arranged a second switch valve 4B that also comprises a pivotshaft 56 actuated by the actuator, a body holder 57 integral with pivotshaft 56 and a flat rectangular valve body 58 fitted to body holder 57.

Thus, first switch valve 4A functions to selectively open and close thepaired openings 52 and 55 at the same time, and second switch valve 4Bfunctions to selectively open and close the other paired openings 53 and54 at the same time. That is, first switch valve 4A functions toselectively open and close a communication between a group of cylinders#1 and #4 and one passage 3A, and second switch valve 4B functions toselectively open and close a communication between the other group ofcylinders #2 and #3 and the other passage 3B, as is understood from thedrawing.

When first switch valve 4A assumes the close position, a communicationbetween the paired openings 52 and 55 is also blocked and thus acommunication between main exhaust passage 2 for cylinder #1 and mainexhaust passage 2 for cylinder #4 is blocked, and when second switchvalve 4B assumes the close position, a communication between the pairedopenings 53 and 54 is also blocked and thus a communication between mainexhaust passage 2 for cylinder #2 and main exhaust passage 2 forcylinder #3 is blocked.

When first and second switch valves 4A and 4B are opened, the exhaustgas from cylinders #1 and #4 is led into first intermediate main exhaustpassage 3A, and at the same time, the exhaust gas from cylinders #2 and#3 is led into second intermediate main exhaust passage 3B.

As will be described in detail hereinafter, a link mechanism actuated bythe single actuator is arranged between the respective pivot shafts 56of first and second switch valves 4A and 4B, so that these two valves 4Aand 4B assume their open and close positions synchronously.

FIG. 7 shows the detail of the link mechanism actuated by the singleactuator 64. The link mechanism comprises a first link plate 61A fixedto pivot shaft 56 of first switch valve 4A, a second link plate 61Bfixed to pivot shaft 56 of second switch valve 4B, a rod 62 having oneend pivotally connected to first link plate 61A and the other endpivotally connected to second link plate 61B, and a third link plate 63fixed to pivot shaft 56 of first switch valve 4A. As shown, first andsecond link plates 61A and 61B are arranged to define therebetween anangle of 90 degrees. The actuator 64 may be of a vacuum power type or anelectromagnetic type, which has an output member connected to third linkplate 63 through a rod 65. When the actuator 64 is energized, the outputmember of the same pushes rod 65. With this, pivot shaft 56 of firstswitch valve 4A is turned clockwise in FIG. 7 and at the same time pivotshaft 56 of second switch valve 4B is turned counterclockwise, and thus,first and second switch valves 4A and 4B assume their close position.

Referring to FIG. 8, there is shown a valve unit 5B that is installed inan exhaust system 200 of a second embodiment of the present invention.For easy understanding of this embodiment, the drawing is schematicallyillustrated with some illustration contradiction.

Valve unit 5B employed in this embodiment 200 has two butterfly valves70 for the respective switch valves 4A and 4B.

Each butterfly valve 70 comprises a pivot shaft 71 that is arranged atan upstream end portion of the corresponding passage 3A or 3B. Eachpivot shaft 71 has two flat valve bodies 72 a and 72 b that extendradially outward therefrom. As shown, flat valve bodies 72 a and 72 bare somewhat offset with respect to an axis of the pivot shaft 71.

A partition wall 73 extends axially in the upstream end portion of eachpassage 3A or 3B to a position near the corresponding pivot shaft 71,and thus the upstream end portion is divided into two passages 52A and55A (or 53A and 54A) which are merged with openings 52 and 55respectively (or openings 53 and 54).

Seal members 74 are secured to inner wall of each passage 3A or 3B. Asshown, when switch valve 4A or 4B takes its close position, the two flatvalve bodies 72 a and 72 b close downstream ends of the two passages 52Aand 55A (or 53A and 54A), respectively. Under this condition, each valvebody 72 a or 72 b is in contact with the corresponding seal member 74.

That is, when first switch valve 4A assumes the close position, thecommunication between each of the paired openings 52 and 55 and thepassage 3A is blocked and at the same time, the communication betweenthe paired openings 52 and 55 is also blocked. Similarly, when secondswitch valve 4B assumes the close position, the communication betweeneach of the paired openings 53 and 54 and the other passage 3B isblocked and at the same time, the communication between the pairedopenings 53 and 54 is blocked. Although not shown in the drawing, a linkmechanism actuated by an actuator is incorporated with both pivot shafts71 to synchronously actuate the same.

Referring to FIG. 9, there is shown a valve unit 5C that is installed inan exhaust system 300 of a third embodiment of the present invention.Also, this drawing is schematically illustrated with some illustrationcontradiction for easy understanding of the embodiment.

Valve unit 5C employed in this embodiment 300 is substantially the sameas valve unit 5B of the above-mentioned embodiment 200, except that inthis third embodiment 300, there is no means corresponding to partitionwalls 73 and in this third embodiment 300, two flat valve bodies 72 aand 72 b extend radially outward from pivot shaft 71. Thus, in thisembodiment 300, even when each switch valve 4A or 4B takes the closeposition as shown, the fluid communication between the paired openings52 and 55 (or 53 and 54) is kept unlike the case of the above-mentionedfirst and second embodiments 100 and 200.

Referring to FIG. 10, there is shown a valve unit 5D that is installedin an exhaust system 400 of a fourth embodiment of the presentinvention. Also, this drawing is schematically illustrated with someillustration contradiction for easy understanding.

Valve unit 5D employed in this embodiment 400 has only one butterflyvalve 80 that serves as both switch valves 4A and 4B for controlling thefluid communication between the four upstream main exhaust passages 2and the two intermediate main exhaust passages 3A and 3B.

Butterfly valve 80 comprises a pivot shaft 81 that is arranged at anupstream portion of the two intermediate main exhaust passages 3A and3B. In the illustrated embodiment, pivot shaft 81 is rotatably supportedby the axially extending partition wall 59. Pivot shaft 81 has two flatvalve bodies 82 a and 82 b that extend radially outward therefrom.However, actually, flat valve bodies 82 a and 82 b are somewhat offsetwith respect to an axis of pivot shaft 81, as shown.

Seal members 84 are secured to inner walls of the passages 3A and 3B. Asshown, when butterfly valve 80 takes its close position, the outsideends of two flat valve bodies 82 a and 82 b are in contact with sealmembers 84. When turning in the direction of the arrows, butterfly valve80 takes an open position.

As is understood from the drawing, when butterfly valve 80 takes theclose position, the fluid communication between the paired openings 52and 55 (or 53 and 54) and first or second intermediate main exhaustpassage 3A or 3B is blocked while keeping the communication between thepaired openings 52 and 55, that is, the communication between the twoupstream main exhaust passages 2 for cylinders #1 and #4. While, whenbutterfly valve 80 turns to the open position, the fluid communicationbetween the paired openings 52 and 55 (or 53 and 54) and first or secondintermediate main exhaust passage 3A or 3B becomes established.

Referring to FIG. 11, there is shown a valve unit 5E that is employed inan exhaust system 500 of a fifth embodiment of the present invention.Like the above-mentioned drawings of FIGS. 8 to 10, the drawing of thisembodiment is schematically illustrated with some illustrationcontraction for easy understanding.

Valve unit 5E employed in this embodiment 500 uses two slide door typevalves 90 as switch valves 4A and 4B. Each slide door type valve 90comprises a flat slide door 91 that is arranged behind the pairedopenings 52, 55, 53 and 54 to slide in a direction perpendicular to theaxes of the intermediate main exhaust passages 3A and 3B.

Referring to FIG. 12, there is shown an exhaust system 600 of a sixthembodiment of the present invention.

As is seen from this drawing, exhaust system 600 of this embodiment issimilar to exhaust system 100 of the above-mentioned first embodiment.Thus, only parts or portions that are different from those of the firstembodiment 100 will be described in detail in the following.

In this sixth embodiment 600, a switch valve 4 is installed in each ofupstream main exhaust passages 2. Each switch valve 4 is arranged in thecorresponding passage 2 as upstream as possible in order that thecorresponding upstream bypass exhaust passage 11 can get a highertemperature exhaust gas after the cold starting of the engine. Actually,the four branches 41, 42, 43 and 44 (or 2) (see FIGS. 3 and 4) ofexhaust manifold 34 have a considerably higher thermal capacity, andthus, if the length of each branch 41, 42, 43 or 44 defined from aninlet end of the same to the corresponding switch valve 4 is large, theexhaust gas led to the corresponding bypass exhaust passage 11 issubjected to a marked temperature drop, which is undesirable toauxiliary catalytic converter 18.

Referring to FIGS. 13 and 14, there is schematically shown an exhaustsystem 700 of a seventh embodiment of the present invention. In thisembodiment 700, auxiliary catalytic converter 18 is directly connectedto cylinder head 33 of the engine 31 in order to shorten the length ofthe four bypass exhaust passages 11. As shown, in this case, four bypassexhaust passages 11 are defined in cylinder head 33, and each bypassexhaust passage 11 is branched from the corresponding exhaust port 100that constitutes part of upstream main exhaust passage 2.

As is seen from FIG. 14, four bypass exhaust passages 11 are joined attheir downstream ends and directly connected to the inlet of auxiliarycatalytic converter 18. In this case, a much higher temperature exhaustgas can be led to the converter 18 even just after cold staring of theengine 31.

Although, in the foregoing description, the present invention isdescribed on the in-line four cylinder internal combustion engine 31,the present invention is widely applicable to various types ofmulti-cylinder internal combustion engine including in-line type andV-type.

The entire contents of Japanese Patent Applications 2004-169394 filedJun. 8, 2004 and 2004-205357 filed Jul. 13, 2004 are incorporated hereinby reference.

Although the invention has been described above with reference to theembodiments of the invention, the invention is not limited to suchembodiments as described above. Various modifications and variations ofsuch embodiments may be carried out by those skilled in the art, inlight of the above description.

1. An exhaust system of a multi-cylinder type internal combustionengine, comprising: a plurality of upstream main exhaust passagesconnected to cylinders of the engine respectively; a downstream mainexhaust passage that is connected to the upstream main exhaust passages;a main catalytic converter mounted in the downstream main exhaustpassage; a plurality of upstream bypass exhaust passages; a downstreambypass exhaust passage that is connected to the upstream bypass exhaustpassages, the downstream bypass exhaust passage having a downstream endconnected to the downstream main exhaust passage at a position upstreamof the main catalytic converter; an auxiliary catalytic convertermounted in the downstream bypass exhaust passage; and a gas flowswitching device that is capable of forcing the exhaust gas from thecylinders of the engine to flow toward the upstream bypass exhaustpassages when assuming a given operation position, in which the gas flowswitching device comprises switch valves that are operatively mounted inthe upstream main exhaust passages, respectively, and configured toclose the upstream main exhaust passages when assuming given operationpositions, respectively, wherein the plurality of upstream bypassexhaust passages respectively extend from the upstream main exhaustpassages and wherein each upstream bypass exhaust passage has asectional area smaller than that of the corresponding upstream mainexhaust passage, and wherein a branched portion of each upstream mainexhaust passage from which the upstream bypass exhaust passage extendsis provided away from a rear end of the upstream main exhaust passage,and the switch valves are located at the rear ends of the upstream mainexhaust passages.
 2. An exhaust system as claimed in claim 1, in whichthe upstream bypass exhaust passages extend from upstream portions ofthe upstream main exhaust passages respectively.
 3. An exhaust system asclaimed in claim 1, in which the downstream main exhaust passage isprovided by joining the upstream main exhaust passages together.
 4. Anexhaust system as claimed in claim 1, in which the downstream bypassexhaust passage is provided by joining the upstream bypass exhaustpassages together.
 5. An exhaust system as claimed in claim 1, in whichtwo of the upstream main exhaust passages are united at their downstreamends to constitute an intermediate main exhaust passage that has adownstream end connected to an upstream end of the downstream mainexhaust passage, and in which the two upstream main exhaust passages arethose extending from the cylinders whose firing order is not successive.6. An exhaust system as claimed in claim 1, further comprising: a firstintermediate main exhaust passage that is arranged between a junctionportion of downstream ends of two upstream main exhaust passages and anupstream end of the downstream main exhaust passage, the two upstreammain exhaust passages being those extending from the cylinders whosefiring order is not successive, and a second intermediate main exhaustpassage that is arranged between a junction portion of downstream endsof the other two upstream main exhaust passages and the upstream end ofthe downstream main exhaust passage, the other two upstream main exhaustpassages being those extending from the cylinders whose firing order isnot successive.
 7. An exhaust system as claimed in claim 1, in whicheach of the upstream main exhaust passages comprises an exhaust portdefined in a cylinder head of the engine and in which each of theupstream bypass exhaust passages extends through the cylinder head toconnect to the exhaust port.
 8. An exhaust system as claimed in claim 1,in which the upstream main exhaust passages comprise branches of anexhaust manifold, and in which the upstream bypass exhaust passages haveupstream ends exposed to upstream portions of the branches of theexhaust manifold respectively.
 9. An exhaust system as claimed in claim1, in which each of the upstream bypass exhaust passages is branchedfrom the corresponding upstream main exhaust passage in a manner todefine an arcuate angle therebetween thereby to smooth the exhaust gasflow from the main exhaust passage to the bypass exhaust passage.
 10. Anexhaust system as claimed in claim 1, in which each of the upstreambypass exhaust passages has a sectional area smaller than that of thecorresponding upstream main exhaust passage thereby to reduce an exhaustinterference which would occur when the cylinders are communicated withone another.
 11. An exhaust system as claimed in claim 1, in which thegas flow switching device is arranged to selectively open and close amain exhaust passage way that includes the upstream main exhaustpassages and the downstream main exhaust passage.
 12. An exhaust systemas claimed in claim 11, in which the gas flow switching device comprisesswitch valves that are operatively mounted in the upstream main exhaustpassages respectively.
 13. An exhaust system as claimed in claim 11, inwhich the gas flow switching device comprises a switch valve that isoperatively installed in a portion where downstream ends of two of theupstream main exhaust passages are joined together, the two upstreammain exhaust passages being those extending from the cylinders whosefiring order is not successive.
 14. An exhaust system as claimed inclaim 13, in which the switch valve is arranged to open a fluidcommunication between the two upstream main exhaust passages when theswitch valve assumes its close position blocking a fluid communicationbetween an upstream zone upstream of the switch valve and a downstreamzone downstream of the switch valve.
 15. An exhaust system as claimed inclaim 13, in which the switch valve is arranged to block a fluidcommunication between the two upstream main exhaust passages when theswitch valve assumes its close position blocking a fluid communicationbetween an upstream zone upstream of the switch valve and a downstreamzone downstream of the switch valve.
 16. An exhaust system as claimed inclaim 15, in which the switch valve comprises a pivotal flat valve bodythat is arranged to synchronously and selectively open and close aplurality of mutually adjacent openings to which downstream ends of theupstream main exhaust passages are connected.
 17. An exhaust system asclaimed in claim 15, in which the switch valve comprises a butterflyvalve that includes a pivot shaft and two flat valve bodies that extendradially outward from the pivot shaft, the butterfly valve beingarranged to synchronously and selectively open and close two mutuallyadjacent openings to which downstream ends of two of the upstream mainexhaust passages are connected, the two upstream main exhaust passagesbeing those extending from the cylinders whose firing order is notsuccessive.
 18. An exhaust system of an in-line four cylinder internalcombustion engine, comprising: first, second, third and fourth upstreammain exhaust passages extending from first, second, third and fourthcylinders of the engine, the first and fourth cylinders being thosewhose firing order is not successive and the second and third cylindersbeing those whose firing order is not successive; a first intermediatemain exhaust passage that is provided by joining downstream ends of thefirst and fourth upstream main exhaust passages; a second intermediatemain exhaust passage that is provided by joining downstream ends of thesecond and third upstream main exhaust passages; a downstream mainexhaust passage that is provided by joining downstream ends of the firstand second intermediate main exhaust passages; a main catalyticconverter mounted in the downstream main exhaust passage; first andsecond upstream bypass exhaust passages respectively extending fromupstream portions of the first and second upstream main exhaustpassages; third and fourth upstream bypass exhaust passages respectivelyextending from upstream portions of the third and fourth upstream mainexhaust passages; a first intermediate bypass exhaust passage that isprovided by joining downstream ends of the first and second upstreambypass exhaust passages; a second intermediate bypass exhaust passagethat is provided by joining downstream ends of the third and fourthupstream bypass exhaust passages; a downstream bypass exhaust passagethat is provided by joining downstream ends of the first and secondintermediate bypass exhaust passages, the downstream bypass exhaustpassage having a downstream end connected to the downstream main exhaustpassage at a position upstream of the main catalytic converter; anauxiliary catalytic converter mounted in the downstream bypass exhaustpassage; a first switch valve that selectively opens and closes a fluidcommunication between each of the first and fourth upstream main exhaustpassages and the first intermediate main exhaust passage; and a secondswitch valve that selectively opens and closes a fluid communicationbetween each of the second and third upstream main exhaust passages andthe second intermediate exhaust passage, in which the first and secondswitch valves are integrally mounted in a valve unit, in which an inletopening of an exhaust gas recirculation system is exposed to an interiorof the auxiliary catalytic converter to introduce thereinto the gasflowing in the auxiliary catalytic converter.